1. Field of the Invention
The invention relates to the generation of infrared laser radiation from a molecular gas, in particular from transitions between the 02.sup.0 0 level and the 01.sup.1 0 level, as well as transitions between the 10.sup.0 0 and 01.sup.1 0 vibrational levels of the CO.sub.2 molecule.
2. Description of the Prior Art
Since their discovery, lasers have been used increasingly for commercial application. High efficiency, high power output, and simplicity of operation are desirable system characteristics for such lasers. Recently, attention has been focused upon the potential use of lasers for separation of isotopes, particularly isotopes of uranium. An important quality of the laser for achieving isotope separation is the spectral coincidence of the laser emission with an absorption line of a single isotope. A strong absorption band of uranium hexafluoride (UF.sub.6) is centered at a wavelength of approximately 16 micrometers (.mu.m). Lasers of adequate quality are not presently available at this wavelength for uranium isotope separation or, in general, at any wavelength between 12 .mu.m and 20 .mu.m for other applications.
Previous work with CO.sub.2 lasers on transitions which produce wavelengths of approximately 9.4 .mu.m and 10.6 .mu.m has been extensive. However, despite a decade of active research which focused on these laser transitions, the possibility of using stimulated emission at these wavelengths to excite 14 .mu.m or 16 .mu.m laser emission from transitions to the 01.sup.1 0 vibrational level was not suggested.
Infrared laser radiation at wavelengths near 14 .mu.m and 16 .mu.m has been obtained previously from a CO.sub.2 gas. Approaches for generating such laser radiation have been directed to the vibrational levels of the CO.sub.2 molecules at energies above that of the 00.sup.0 1 level. Laser emission from transition to vibrational levels at lower energies, specifically to the 01.sup.1 0 level, has not been considered feasible for several reasons. It was generally thought that the collisional lifetimes of these lower energy vibrational levels of the CO.sub.2 molecules were short compared to the time required to achieve a population inversion between the desired lasing levels. However, recent evidence suggests that the lifetimes of these levels are long enough to support a population inversion. Furthermore, conventional means for selectively pumping the desired levels were ineffective since such means typically populated the 01.sup.1 0 level, the lower level of the lasing transitions. This problem is circumvented by exciting the laser transitions using transfer by stimulated emission from a level which can be selectively pumped. Adding to the complexity of the problem is the proximity of the 01.sup.1 0 level to the ground state. At room temperature, this level exhibits a relatively high thermal population. This increases the threshold conditions for achieving successful laser operation. The thermal population of the 01.sup.1 0 level can be reduced by cooling the gas mixture.
A technique for generating 16 .mu.m laser radiation is discussed by R. M. Osgood, Jr., "Optionally Pumped 16 .mu.m CO.sub.2 Laser", Appl. Phys. Lett. 28, 342, 1976.